In modern times, there has been a proliferation of electronic equipment placed in use by business and industry. Many of such electronic devices require electrical interconnects between use stations or terminal boxes. In many cases, these electrical interconnects utilize an ensemble of individual wires bundled as a cable or "wiring harness" to provide a plurality of inputs and outputs for the connected devices. By way of example, but not limitation, such electrical interconnects are commonly found within networked computer systems, between a central processing unit and its accessory electronic devices (printers, modems, display screens, etc.), telephone communications equipment, music entertainment systems and the like. In order to facilitate interconnection of these various electronic devices, the interconnects are often provided with multi-terminal plugs at each of their ends which plugs may then be inserted into the respective electronic apparatus thus establishing electrical communication therebetween.
The increased use of cable harnesses has resulted in the need for apparatus and methods for testing the integrity of the cable harness and their associated terminal plugs in order to discover a compromised electrical circuit condition within the harness. Such testing is not simply a matter of testing the continuity of each individual wire since short circuits between two wires or caused by defective end plug terminals of the harness may give false continuity readings. As the number of wires increase in a given cable harness, then, the difficulty of testing continuity while eliminating short circuit possibilities increases as to mathematical square of the number of wires to be tested. Thus, where a wiring harness has thirty (30) wires, it is necessary to conduct 900 individual continuity checks to ensure proper functioning of the cable harness. This even assumes that it is convenient to have access to the opposite ends of the cable harness at a single test location.
As a result of the need for better cable harness testing techniques, there has been developed different test apparatus for cable harnesses. Most of these devices, however, require the presence, at a single location, of both ends of the cable harness to be tested. Both ends of the cable are electrically connected to the device and the device then scans the individual wires in the cable harness in order to detect open circuit paths and short circuits. Naturally, where a cable harness is extensive in length or where it is mounted internally of walls or other equipment, the retrieval of both ends of the cable to a common location is often not practicable.
Another testing device has sought to eliminate the problem of the presence of both cable ends at a single location by utilizing a shorting terminal plug placed on one end of the cable harness to be tested while the testing device is placed at the other end. The shorting plug establishes one wire of the cable harness to be a dedicated return path for test signals that interrogate remaining wires. While this device provides some improvement, it has corresponding problems. For example, if the wire defining the dedicated return path is defective, the test operator will then have to test several wires before determining whether the dedicated return wire is defective or whether other wires in the cable harness have malfunctions. Further, determination of shorts between wires is difficult, indeed, where there are very long cables, any indication of shorts may be ambiguous.
Accordingly, there remains a need within the industry for imprived apparatus and methods for testing the integrity of cable harnesses. This need is felt by testing technicians, installers of equipment and even quality control personnel for manufacturing companies. There is a further need for such devices which are easy to use and inexpensive in cost.